The most important legal issue at this time is of jurisdiction. According to the UN Convention of the Law of the Sea (UNCLOS) of which both India and Italy are signatories, the coastal state (India) has jurisdiction in its territorial waters (12 nautical miles from the shoreline) for ships engaged in innocent passage. Because it’s hard to draw boundary lines in the water, UNCLOS recognises a contiguous zone that extends a further 12 nautical miles beyond the territorial waters where the coastal state can visit, board and arrest ships suspected of criminal activity in its territorial waters.

What if the crime has been committed in international waters? In general, UNCLOS treats the ship as sovereign territory of the country whose flag it flies and therefore under its jurisdiction. For warships, this is explicit and unambiguous. Even so, there are grounds for another state to claim jurisdiction, invoking its domestic laws or broader principles of international law. [See this explainer at Straight Dope] In effect, this really depends on the relative power of the states concerned—the United States may be able to assert a principle that say, the Republic of Nauru cannot.

Girone and Massimiliano, members of the navy security team of Italian merchant vessel Enrica Lexie, in Kochi. Reuters

Once jurisdiction is established, the respective legal processes take over: evidence must be produced, culpability established, guilt proven, verdicts given and appeals heard before civil damages are paid or criminal punishments meted out. So until the courts pronounce the verdict, the Italian marines are suspects and must be presumed innocent until proven guilty.

On the jurisdictional matter, what it means is that if it is established that the crime occurred short of 12 nautical miles from the Kerala coast, India has exclusive jurisdiction. If it occurred in international waters, beyond 200 nautical miles from Kerala, Italy does.

But between the two areas lies the exclusive economic zone (EEZ) where there is a balance between the rights of the coastal state and everyone else. This is where perhaps the international lawyers get to make their money. Because UNCLOS says that the coastal state may initiate judicial proceedings on a foreign vessel in “the exercise of its sovereign rights to explore, exploit, conserve and manage the living resources in the exclusive economic zone.” Those who disagree with how a coastal state interprets this can, well, go to the Hague.

This case involves an additional factor: not only were there armed military personnel on board the merchant ship, they were reportedly not under the command of the Enrica Lexie‘s captain. While the ship is ostensibly an oil-tanker this arrangement calls into question whether "innocent passage" and "peaceful purpose" holds. Furthermore, under international law, military personnel are considered state actors. This means the actions of the Italian marines on board the Enrica Lexie, whether or not authorised by the government, are construed to be that of the Italian Republic.

From media reports, the Italian marines might have opened fire too readily even considering the risk of piracy. Their failure to report the incident before being quizzed by the Indian Coast Guard adds to the dubiousness of their conduct.

So far the Indian authorities have acted in consistence with international law. The Coast Guard and police were within their rights to board and arrest suspects on the Enrica Lexie and subject them to the due process under Indian law. If not already, they will almost certainly be allowed consular access and legal defence. The defendants and the Italian government can challenge the court’s jurisdiction by providing evidence of their claim that the incident occurred in the high seas.

It is untenable to claim, as the Italians are doing, that the legal proceedings must take place in Italy on the basis of their claim that the incident took place in international waters. So let the law take its course.

In international relations, legal processes operate to the extent the states involved agree to abide by them. This is a fit case: there was a reason to deploy armed marines on the merchant ship and it is quite unlikely that the Italians were attempting an invasion or infiltration of Kerala. In the absence of hostile or mala fide intents (politically speaking), it is best to agree to pursue the matter soberly in courts of law. Fattening lawyers is far more conducive to international peace than agitating politicians.

Geopolitical questions are decided on the basis of interests and power, with legal principles and processes employed as mere instruments in their pursuit. There is no reason for India to wish for raising tensions with Italy at this time. Italy’s behaviour in the coming weeks will determine whether this feeling is mutual.

Update: Some reports suggest that the Italian delegation claimed that the marines have diplomatic immunity because they are naval officers. That’s ridiculous.